A vehicle may include a three-way catalyst (TWC) for treating exhaust gases of an internal combustion engine. Feedback control may be applied to regulate an engine's air-fuel ratio so that engine exhaust constituents may be adjusted in a way that improves catalyst efficiency. Some vehicles may include a universal exhaust gas oxygen (UEGO) sensor positioned upstream of the TWC and a heated exhaust gas oxygen (HEGO) sensor positioned downstream of the TWC to control the AFR near stoichiometry. The UEGO sensor provides feedback to adjust engine out gases about stoichiometry. The HEGO sensor provides feedback to bias the engine air-fuel ratio richer or leaner to improve catalyst efficiency.
Precise engine air-fuel ratio control may improve catalyst conversion efficiency; however, if the catalyst is in a degraded state, vehicle emissions may be above regulated levels even if the engine air-fuel ratio is precisely controlled. Therefore, it may be desirable to determine whether or not a catalyst is degraded so that remedial measures may be taken to bring the vehicle back within a regulated emissions level or to alert the driver to take the vehicle to a dealership for repair.
One way to judge whether or not a catalyst is degraded is to make a one-time change to the engine's air fuel ratio from lean to rich or vise-versa and measure the time it takes to observe a corresponding change in exhaust gas oxygen concentration downstream of a catalyst. The time it takes to observe a change in oxygen concentration may provide an indication as to a level of catalyst degradation. However, engine exhaust emissions may be degraded if rich or lean exhaust gases break through the catalyst due to intrusive changes in the engine's air-fuel ratio. Further, opportunities to monitor a step change may be limited and noise in the system may make the estimated results based on only a few observations less certain.
The inventors have recognized the above-mentioned disadvantages and have developed a method, comprising: during feedback engine air-fuel ratio control responsive to a downstream of a catalyst exhaust gas sensor: indicating degradation of the catalyst in response to a catalyst transfer function determined only within a specified frequency range based on the exhaust gas sensor output.
By determining a catalyst's transfer function only within a specified frequency range, it may be possible to provide the technical result of assessing catalyst degradation via engine air-fuel ratio modulation used to improve catalyst efficiency. In other words, a catalyst degradation assessment may be provided based on small air-fuel ratio variations routinely used to improve catalyst efficiency rather that via a specialized perturbation that may result in emission breakthrough. As a result, an assessment of catalyst degradation may be possible in a way that does not degrade vehicle emissions and may be more robust to many sources of noise.
The present description may provide several advantages. In particular, the approach may improve vehicle catalyst diagnostics. Additionally, the approach may provide improved vehicle emissions by providing an indication of a condition of catalyst degradation. Further, the approach may provide a catalyst diagnostic that is not intrusive or noticeable by a driver.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.